1. Field of the Invention
The present invention relates to a vehicle body slip angle detecting apparatus that detects a vehicle body slip angle which is an angle made by the direction of the vehicle body (i.e., longitudinal direction of the vehicle body) and the advancing direction of the vehicle body, a vehicle body slip angle detecting method, and a vehicle motion control apparatus provided with the vehicle body slip angle detecting apparatus.
2. Description of the Related Art
Conventionally, there has been widely known a vehicle motion control apparatus that performs a vehicle stabilization control (e.g., over-steer suppression control) in order to maintain running stability of the vehicle when the vehicle is in the turning state and the vehicle body slip angle becomes not less than a predetermined value. Accordingly, it is necessary to precisely obtain the vehicle body slip angle in order to precisely start and execute the above-mentioned vehicle stabilization control.
In general, the vehicle body slip angle is estimated on the basis of the vehicle body speed, lateral acceleration detected by a lateral acceleration sensor, yaw rate detected by a yaw rate sensor, and a known given equation that requires a time integrated calculation. However, an error is likely to occur in the time integrated calculation. Therefore, it is difficult to precisely estimate the vehicle body slip angle by this technique.
In recent years, a camera for photographing the road surface on which the vehicle is running is fixed to a predetermined position of the vehicle body, and attempts have been made to detect the vehicle body slip angle by utilizing the image photographed by the camera, as disclosed in Japanese Unexamined Patent Application No. 2000-81322.
More specifically, the above-mentioned reference discloses a technique for detecting the vehicle body slip angle on the basis of the flow direction of the road surface in the image by utilizing that the flow of the road surface during the exposure time of the camera appears on the image of the road surface.
In order to precisely detect the vehicle body slip angle (in particular, very small slip angle) by adopting this technique, it is necessary to precisely obtain the flow direction of the road surface in the image thereof. For this, it is necessary to sufficiently secure the range (particularly, the length of the road surface in the longitudinal direction of the vehicle body in the image thereof) of the road surface on the image thereof.
However, it is generally difficult to sufficiently secure the road surface on the image thereof photographed by the camera fixed to the vehicle body. Therefore, it is also difficult to precisely estimate the vehicle body slip angle (in particular, a very small slip angle) with the technique disclosed in the aforesaid reference.